Preparation method of macro-meso-microporous molecular sieve catalyst wrapped with noble metal and application thereof

Abstract

The application discloses a preparation method of a large-inter-micropore molecular sieve catalyst coated with noble metal, and belongs to the technical field of catalysts.The preparation method comprises the following steps: 1) adding a silicon source and an aluminum source into deionized water, uniformly stirring, then adding a noble metal precursor and an alkaline precipitator to make the system alkaline, continuously stirring, and then filtering and drying to obtain a silicon-aluminum precursor loaded with the noble metal; the silicon source comprises an amino-substituted silane; 2) dipping the silicon-aluminum precursor loaded with the noble metal into a water solution of a structure-directing agent and drying and concentrating to obtain an initial gel; crystallizing the initial gel, then cooling to room temperature, and then performing water washing, drying and calcining on the obtained solid product to obtain the large-inter-micropore ZSM-5 molecular sieve catalyst coated with the noble metal.The catalyst prepared by the method has high activity and selectivity in a normal paraffin (C>=6) hydroisomerization reaction, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve catalyst preparation technology, specifically relating to a method for preparing and applying a macro-meso-microporous molecular sieve catalyst encapsulating noble metals. Background Technology

[0002] Noble metal catalysts have attracted widespread attention due to their excellent catalytic performance in various catalytic reactions. However, their practical applications are still limited because they are prone to deactivation due to sintering under high-temperature reaction conditions. Supported noble metal catalysts, prepared by loading noble metals onto porous supports, can effectively improve the thermal stability and catalytic activity of noble metals, making them important for applications in petroleum refining, environmental protection, and other fields. Molecular sieves are crystalline materials with unique pore structures. Due to their excellent characteristics such as strong acid centers, large specific surface area, strong ion exchange capacity, and high thermal and hydrothermal stability, they are widely used as porous supports in industrial reactions. Encapsulating noble metals within the pores of molecular sieves can inhibit the aggregation and growth of noble metal nanoparticles through the confinement effect of the pores, delaying sintering deactivation and ensuring that the noble metal catalyst maintains high catalytic activity under reaction conditions. On the one hand, due to the small pore size of molecular sieves, it is difficult to encapsulate noble metals within the pores. On the other hand, the small pore size and single pore structure of traditional microporous molecular sieves hinder the proximity of reactants to active sites, limiting the diffusion of reactants and products and reducing catalytic efficiency. Considering that hierarchical molecular sieves possess abundant pore structures, exposing more active sites, and thus facilitating the diffusion of reactants and products, encapsulating noble metals within hierarchical molecular sieves holds promise for further improving the activity of noble metal / molecular sieve catalysts.

[0003] Currently, commonly used methods for preparing noble metal-supported molecular sieve catalysts include impregnation, ion exchange, and isomorphic transformation. However, these methods have drawbacks. First, the noble metals are mostly distributed on the surface of the molecular sieve, making them prone to sintering and agglomeration at high temperatures, thus reducing stability. Second, the preparation of hierarchical porous molecular sieves often requires the introduction of additional soft templates or hard membranes, making the synthesis process cumbersome. Therefore, finding a suitable synthesis method to encapsulate noble metals within the channels of hierarchical porous molecular sieves is of great significance for the development of noble metal-supported molecular sieve catalysts.

[0004] Patent CN201611095667.X provides a method for preparing a large-mesh microporous molecular sieve membrane on the inner surface of a metal channel, as well as the channel and its application. The molecular sieve catalyst membrane uses a transparent liquid containing sodium hydroxide, aluminum and silicon precursors, water and organic amines as the molecular sieve membrane synthesis liquid, and a metal channel such as a nickel-based high-temperature alloy as the carrier.

[0005] Patent CN201610642477.9 discloses a diatomaceous earth / nano-TS-1 titanium silicate zeolite composite material with a multi-level porous structure and its preparation method. Using inexpensive diatomaceous earth as a carrier, nano-TS-1 titanium silicate zeolite is uniformly loaded onto the surface of diatomaceous earth through electrostatic reversal adsorption nucleation crystallization, thus obtaining a diatomaceous earth / nano-TS-1 titanium silicate zeolite composite material with a multi-level porous structure containing large / medium / micropores, and has a large specific surface area and high total pore volume.

[0006] Patent CN201810685748.8 discloses a method for preparing a pore-tunable Fe-based metal-organic framework-phosphotungstic acid. The preparation method is as follows: FeCl3·6H2O, 2-aminoterephthalic acid, phosphotungstic acid, hexadecyltrimethylammonium bromide and TMB are added simultaneously, mixed and stirred evenly, and reacted at a constant temperature using a hydrothermal method. After centrifugation, washing and drying, a pore-tunable Fe-based metal-organic framework-PTA is obtained. The pore size of the catalyst of this invention can be tuned within different ranges of micropores, mesopores and macropores.

[0007] Patent CN201810938062.5 discloses a noble metal catalyst for the isomerization of n-alkanes, its preparation method, and its application. It uses a ZSM-5 and SAPO-11 composite molecular sieve as a support, adjusts the support structure with a cerium source, and uses a noble metal acid or noble metal chloride as the active component raw material. The loading of the noble metal is 0.1–5 wt.%; the mass percentage of the cerium source is 0.01–3 wt.%; the noble metal is one or a mixture of Pt and Pd. This patent uses a traditional impregnation method to load the metal.

[0008] Patent CN93119747.3 discloses an alkyl aromatic hydrocarbon isomerization catalyst, which uses a composite zeolite composed of ZSM-5 zeolite and mordenite and alumina as a support, and carries a Group VIII noble metal. When this catalyst is used for the isomerization of C8 aromatic hydrocarbons, the concentration of p-xylene in xylene in the product reaches or approaches the thermodynamic equilibrium value, the xylene yield is high, and at the same time, it can convert a large amount of ethylbenzene to selectively generate benzene.

[0009] Patent CN202010707279.2 discloses a hydroisomerization catalyst, its preparation method, and its application. The catalyst comprises aluminum hydroxide gel, HY molecular sieve, HZSM-5 molecular sieve, and noble metals and rare earth elements. The preparation method involves mixing alumina and the two types of molecular sieves, followed by impregnation to load the noble metals onto a solid catalyst. However, this method results in uneven mixing of the alumina and molecular sieves, and uneven distribution of the noble metals on the support, leading to agglomeration.

[0010] Patent CN201510750240.8 discloses an isomerization catalyst, its preparation method, and its application. The catalyst contains an MCM-22 / ZSM-23 composite molecular sieve, gallium oxide, and a Group VIII noble metal active component. In contrast, the composite molecular sieve in the comparative literature is a microporous molecular sieve with low mass transfer efficiency; the noble metal active component is mostly distributed on the outer surface of the molecular sieve, making it prone to sintering and exhibiting poor stability.

[0011] Patent CN202111144194.9 discloses a method for preparing a Pd / ZSM-5 catalyst. This method involves mixing water, anhydrous ethanol, and organosilicon ester, adjusting the pH to 1-4 with sulfuric acid, then adding a palladium precursor solution and stirring until homogeneous. Tetramethylammonium hydroxide and boehmite are then added to form a milky white gel. The gel is subjected to a hydrothermal reaction, and the resulting solid product is reduced under a hydrogen atmosphere to obtain the Pd / ZSM-5 catalyst. When preparing the Pd / ZSM-5 catalyst using this technique, under acidic conditions (pH 1-4), the organosilicon ester undergoes rapid hydrolysis and polymerization, leading to easy phase separation between the noble metal precursor solution and the gel, resulting in uneven distribution of the noble metal and easy agglomeration. Summary of the Invention

[0012] The purpose of this invention is to provide a method for preparing a macro-meso-microporous molecular sieve catalyst encapsulating noble metals. This method can encapsulate noble metals within the channels of a hierarchical ZSM-5 molecular sieve, thereby improving the resistance of the noble metals to sintering and enabling them to maintain high catalytic activity at higher temperatures.

[0013] Another objective of this invention is to provide an application of a macro-meso-microporous molecular sieve catalyst encapsulating precious metals.

[0014] To achieve the above objectives, the present invention provides a method for preparing a macro-meso-microporous molecular sieve catalyst encapsulating noble metals, comprising the following steps:

[0015] 1) Preparation of silicon-aluminum precursors loaded with noble metals

[0016] A silicon source and an aluminum source are added to deionized water and stirred until homogeneous. Then, a noble metal precursor and an alkaline precipitant are added to make the system alkaline. Stirring continues, followed by filtration and drying to obtain a silicon-aluminum precursor loaded with noble metals. The silicon source contains amino-substituted silanes.

[0017] 2) Preparation of macro-meso-microporous ZSM-5 molecular sieve catalysts encapsulated with noble metals

[0018] The silicon-aluminum precursor loaded with noble metals obtained in step 1) was impregnated with an aqueous solution of a structure-directing agent and dried and concentrated to obtain an initial gel; the initial gel was crystallized and then cooled to room temperature; the resulting solid product was washed with water, dried and calcined to obtain a macro-meso-microporous ZSM-5 molecular sieve catalyst encapsulating noble metals.

[0019] The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to the present invention is characterized in that the noble metal content in the catalyst is 0.05%-5%, and the molar ratio of SiO2 to Al2O3 is 10-100.

[0020] The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to the present invention is characterized in that the silicon source in step 1) is a mixture of silicon source I and silicon source II, wherein silicon source I is selected from aminopropyltriethoxysilane and / or aminopropyltrimethoxysilane, and silicon source II is selected from at least one of methyl orthosilicate, tetraethyl orthosilicate, silica sol and sodium silicate, and the mass ratio of silicon source I to silicon source II is 1:99 to 1:4.

[0021] The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to the present invention is characterized in that the aluminum source in step 1) is at least one of aluminum isopropoxide, aluminum nitrate, aluminum chloride and boehmite.

[0022] The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to the present invention is characterized in that the noble metal precursor in step 1) is a soluble substance containing Pd, Pt, and Au, wherein the amount of the soluble substance containing Pd, Pt, and Au added is 0.1-10% of the mass of the silicon source.

[0023] The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to the present invention is characterized in that the alkaline precipitant in step 1) is at least one of ammonia, sodium hydroxide, potassium hydroxide, ammonium carbonate and ammonium bicarbonate, and the pH of the system is 9-11.

[0024] The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to the present invention is characterized in that the structure directing agent in step 2) is at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrapropylammonium bromide and tetrapropylammonium chloride, the concentration of the aqueous solution of the structure directing agent is 5-40%, and the mass ratio of the amount of the aqueous solution of the structure directing agent added to the silicon-aluminum precursor loaded with noble metals is 5-15:1.

[0025] The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to the present invention is characterized in that the crystallization conditions in step 2) are crystallization at 100-200℃ for 12-100h.

[0026] The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to the present invention is characterized in that the drying temperature in step 2) is 30-100℃ and the time is 2-12h, and the calcination temperature is 400-600℃ and the time is 2-8h.

[0027] To achieve the above objectives, the present invention also provides the application of the above-described catalyst in the hydroisomerization reaction of n-alkanes with 6 or more carbon atoms.

[0028] Beneficial effects of this invention:

[0029] This invention employs a hydrothermal method to synthesize a silicon-aluminum precursor loaded with noble metals, followed by a dry gel crystallization method to synthesize a macro-meso-microporous molecular sieve catalyst encapsulating the noble metals. The silicon-aluminum precursor serves as both the silicon and aluminum source for the molecular sieve synthesis, and also as a macroporous template for the synthesis of hierarchical porous molecular sieves, ultimately resulting in a macro-meso-microporous molecular sieve catalyst. Furthermore, this method uses a silicon source rich in amino organic groups to anchor the noble metals within the silicon-aluminum precursor, ensuring uniform distribution. Then, the dry gel crystallization method simultaneously encapsulates the noble metals in situ within the molecular sieve crystals during the sieve crystallization process. The noble metal catalyst obtained by this method exhibits high dispersibility and high stability. Additionally, the macro-meso-microporous composite pore structure provides excellent diffusion performance. This method is simple, feasible, and highly versatile, with a wide range of applications.

[0030] The catalyst prepared by this invention exhibits high activity and selectivity in the hydroisomerization reaction of n-alkanes (C≥6), and has good prospects for industrial application. Attached Figure Description

[0031] Figure 1 The XRD patterns of sample M / ZSM-5 prepared in Examples 1-5 and Comparative Examples 1 and 2 are shown.

[0032] Figures 2a to 2g The images shown are SEM images of the samples prepared in Examples 1-5 and Comparative Examples 1 and 2, respectively.

[0033] Figures 3a to 3g The images are TEM images of the samples prepared in Examples 1-5 and Comparative Examples 1 and 2, respectively. Detailed Implementation

[0034] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0035] Example 1

[0036] Under stirring conditions at 50°C, a silicon source comprising 1.0 g tetraethyl orthosilicate and 0.01 g aminopropyltriethoxysilane was added to 60 mL of deionized water. Then, an appropriate amount of aluminum isopropoxide was added based on a SiO2 / Al2O3 molar ratio of 10, and stirring was continued for 1 h. A 0.2 mg / mL chloropalladium solution was added at 0.1% of the silicon source mass, and ammonia was added to adjust the pH of the system to 10. Stirring was continued at 50°C for 2 h. After filtration, washing, water washing, and drying, a silicon-aluminum precursor loaded with the noble metal Pd was obtained, named Pd-1@Si-Al(10). An appropriate amount of tetraethylammonium hydroxide was added to deionized water and stirred to dissolve, yielding a 5% tetraethylammonium hydroxide aqueous solution. Pd-1@Si-Al(10) was impregnated with this tetraethylammonium hydroxide aqueous solution, wherein the mass ratio of the tetraethylammonium hydroxide aqueous solution to Pd-1@Si-Al(10) was 15. After drying at 40°C for 10 h, an initial gel was obtained. The initial gel was placed in a stainless steel high-pressure reactor and crystallized at 100℃ for 100h. The reactor was then cooled to room temperature. The resulting solid product was washed with water and dried in a 100℃ drying oven. Then it was placed in a muffle furnace and calcined at 500℃ for 4h in air atmosphere. Finally, a macro-meso-microporous ZSM-5 molecular sieve catalyst with Pd encapsulated was obtained. The content of Pd was 0.05%. The sample was named Pd-1@ZSM-5(10).

[0037] Example 2

[0038] Under stirring conditions at 50°C, a silicon source consisting of 0.30 g silica sol and 0.25 g aminopropyltriethoxysilane was added to 60 mL of deionized water. Then, an appropriate amount of aluminum nitrate was added based on a SiO2 / Al2O3 molar ratio of 10, and stirring was continued for 1 h. A 0.2 mg / mL chloropalladium acid solution was added at 0.5% of the silicon source mass, and sodium hydroxide was added to adjust the pH of the system to 9. Stirring was continued at 50°C for 2 h. After filtration, washing, water washing, and drying, a silicon-aluminum precursor loaded with the noble metal Pd was obtained, named Pd-2@Si-Al(10). An appropriate amount of tetrapropylammonium hydroxide was added to deionized water and stirred to dissolve, yielding a 5% tetrapropylammonium hydroxide aqueous solution. Pd-2@Si-Al(10) was impregnated with this tetrapropylammonium hydroxide aqueous solution, wherein the mass ratio of the tetrapropylammonium hydroxide aqueous solution to Pd@Si-Al(10) was 15. After drying at 40°C for 10 h, an initial gel was obtained. The initial gel was placed in a stainless steel high-pressure reactor and crystallized at 150℃ for 72 hours. The reactor was then cooled to room temperature. The resulting solid product was washed with water and dried in a 100℃ drying oven. Then it was placed in a muffle furnace and calcined at 500℃ for 4 hours in air atmosphere. Finally, a macro-meso-microporous ZSM-5 molecular sieve catalyst with Pd encapsulated was obtained. The content of Pd was 0.25%. The sample was named Pd-2@ZSM-5(10).

[0039] Example 3

[0040] Under stirring conditions at 50°C, a silicon source consisting of 1.2 g sodium silicate and 0.1 g aminopropyltriethoxysilane was added to 60 mL of deionized water. Then, an appropriate amount of aluminum chloride was added based on a SiO2 / Al2O3 molar ratio of 50, and stirring was continued for 1 h. A 0.2 mg / mL chloropalladium acid solution was added at 1% of the silicon source mass, and potassium hydroxide was added to adjust the pH of the system to 11. Stirring was continued at 50°C for 2 h. After filtration, washing, water washing, and drying, a silicon-aluminum precursor loaded with the noble metal Pd was obtained, named Pd@Si-Al(50). An appropriate amount of tetrapropylammonium bromide was added to deionized water and stirred to dissolve, yielding a 5% tetrapropylammonium bromide aqueous solution. Pd@Si-Al(50) was impregnated with this tetrapropylammonium bromide aqueous solution, wherein the mass ratio of the tetrapropylammonium bromide aqueous solution to Pd@Si-Al(50) was 15. After drying at 40°C for 10 h, an initial gel was obtained. The initial gel was placed directly in a stainless steel high-pressure reactor and crystallized at 180℃ for 36 hours. The reactor was then cooled to room temperature. The resulting solid product was washed with water and dried in a 100℃ drying oven. Then it was placed in a muffle furnace and calcined at 500℃ for 4 hours in air atmosphere. Finally, a macro-meso-microporous ZSM-5 molecular sieve catalyst containing Pd encapsulated with noble metal was obtained. The content of noble metal Pd was 0.5%, and the sample was named Pd@ZSM-5(50).

[0041] Example 4

[0042] Under stirring conditions at 50°C, a silicon source comprising 1.0 g tetraethyl orthosilicate and 0.1 g aminopropyltriethoxysilane was added to 60 mL of deionized water. Then, based on a SiO2 / Al2O3 molar ratio of 100, an appropriate amount of pseudoboehmite was added, and stirring continued for 1 h. 0.2 mg / mL chloroplatinic acid solution was added at 5% of the silicon source mass, and ammonium carbonate was added to adjust the pH of the system to 9. Stirring continued at 50°C for 2 h. The product was filtered, washed, rinsed with water, and dried to obtain a silicon-aluminum precursor loaded with noble metal Pt, named Pt@Si-Al(100). Tetrapropylammonium chloride was added to deionized water and stirred to dissolve, yielding a tetrapropylammonium chloride aqueous solution with a concentration of 20%. The prepared precursor Pt@Si-Al(100) was impregnated with this tetrapropylammonium chloride aqueous solution, wherein the mass ratio of the tetrapropylammonium chloride aqueous solution to Pd@Si-Al(10) was 8. After drying at 40°C for 10 h, an initial gel was obtained. The initial gel was placed in a stainless steel high-pressure reactor and crystallized at 200℃ for 12 hours. The reactor was then cooled to room temperature. The resulting solid product was washed with water and dried in a 100℃ drying oven. Then it was placed in a muffle furnace and calcined at 500℃ for 4 hours in air atmosphere. Finally, a macro-meso-microporous ZSM-5 molecular sieve catalyst with Pt encapsulated was obtained. The content of Pt was 3.0%. The sample was named Pt@ZSM-5(100).

[0043] Example 5

[0044] Under stirring conditions at 50°C, a silicon source consisting of 1.0 g of methyl orthosilicate and 0.2 g of aminopropyltriethoxysilane was added to 60 mL of deionized water. Then, based on a SiO2 / Al2O3 molar ratio of 50, an appropriate amount of boehmite was added, and stirring continued for 1 h. 0.1 mg / mL chloroauric acid solution was added at 10% of the silicon source mass, and ammonium bicarbonate was added to adjust the pH of the system to 9. Stirring continued at 80°C for 0.5 h. The product was filtered, washed, rinsed with water, and dried to obtain a silicon-aluminum precursor loaded with the noble metal Au, named Au@Si-Al(50). An appropriate amount of tetrapropylammonium hydroxide was added to deionized water and stirred to dissolve, yielding a 40% tetrapropylammonium hydroxide aqueous solution. Au@Si-Al(50) was impregnated with this tetrapropylammonium hydroxide aqueous solution, wherein the mass ratio of the tetrapropylammonium hydroxide aqueous solution to Pd@Si-Al(10) was 6. After drying at 40°C for 10 h, an initial gel was obtained. The initial gel was placed in a stainless steel high-pressure reactor and crystallized at 150℃ for 72 hours. The reactor was then cooled to room temperature. The resulting solid product was washed with water and dried in a 100℃ drying oven. Then it was placed in a muffle furnace and calcined at 500℃ for 4 hours in air atmosphere. Finally, a macro-meso-microporous ZSM-5 molecular sieve catalyst with Au encapsulated in noble metal was obtained. The content of noble metal Au was 5.0%. The sample was named Au@ZSM-5(50).

[0045] Comparative Example 1

[0046] Under stirring at 50℃, 1.2 g of tetraethyl orthosilicate was added to 60 mL of deionized water. Then, an appropriate amount of aluminum chloride was added according to a SiO2 / Al2O3 molar ratio of 50, and stirring was continued for 1 h. 0.2 mg / mL chloropalladium acid solution was added at 1% of the silicon source mass, and potassium hydroxide was added to adjust the pH of the system to 9. Stirring was continued for 2 h at 50℃. After filtration, washing, water washing, and drying, a silicon-aluminum precursor loaded with noble metal Pd was obtained, named Pd-3@Si-Al(50). An appropriate amount of tetrapropylammonium bromide was added to deionized water and stirred to dissolve, resulting in a 5% tetrapropylammonium bromide aqueous solution. Pd-3@Si-Al(50) was impregnated with the tetrapropylammonium bromide aqueous solution, wherein the mass ratio of the tetrapropylammonium bromide aqueous solution to Pd-3@Si-Al(50) was 15. After drying at 40℃ for 10 h, an initial gel was obtained. The initial gel was placed directly in a stainless steel high-pressure reactor and crystallized at 180℃ for 36 hours. The reactor was then cooled to room temperature. The resulting solid product was washed with water and dried in a 100℃ drying oven. Then it was placed in a muffle furnace and calcined at 500℃ for 4 hours in air atmosphere. Finally, a microporous ZSM-5 molecular sieve catalyst with Pd encapsulated in noble metal was obtained. The content of noble metal Pd was 0.5%. The sample was named Pd-3@ZSM-5(50).

[0047] Comparative Example 2

[0048] Under stirring conditions at 50°C, a silicon source comprising 1.0 g tetraethyl orthosilicate and 0.01 g aminopropyltriethoxysilane was added to 60 mL of deionized water. Then, based on a SiO2 / Al2O3 molar ratio of 50, an appropriate amount of aluminum isopropoxide was added, and stirring continued for 1 h. A 0.2 mg / mL chloropalladium solution was added at 0.1% of the silicon source mass, and ammonia was added to adjust the pH of the system to 9. Stirring continued at 50°C for 2 h. The product was filtered, washed, rinsed with water, and dried to obtain a silicon-aluminum precursor loaded with the noble metal Pd, named Pd-4@Si-Al(50). An appropriate amount of tetraethylammonium hydroxide was added to deionized water and stirred to dissolve, yielding a 5% tetraethylammonium hydroxide aqueous solution. Pd-4@Si-Al(50) was mixed uniformly with this tetraethylammonium hydroxide aqueous solution to prepare an initial gel, wherein the mass ratio of the tetraethylammonium hydroxide aqueous solution to Pd-4@Si-Al(50) was 15. The initial gel was placed in a stainless steel high-pressure reactor and hydrothermally crystallized at 150℃ for 72 hours. The reactor was then cooled to room temperature. The resulting solid product was washed with water and dried in a 100℃ drying oven. It was then placed in a muffle furnace and calcined at 500℃ for 4 hours in air atmosphere to obtain a catalyst encapsulated with the noble metal Pd. The content of the noble metal Pd was 0.05%, and the sample was named Pd-4@HT-ZSM-5.

[0049] Characterization and performance testing

[0050] The catalysts prepared in Examples 1-5 and Comparative Examples 1-2 were characterized by XRD, and the results are as follows: Figure 1 As shown, the XRD patterns of samples Pd@ZSM-5(10), Pd@ZSM-5(50), Pt@ZSM-5(100), Au@ZSM-5(50), Pd-3@ZSM-5(50), and Pd-4@HT-ZSM-5 are similar to the characteristic spectra of the standard MFI topology. Figure 1 The diffraction peaks were of high intensity, indicating good crystallization. No obvious diffraction peaks of noble metal oxides were observed in the XRD pattern, indicating that the noble metals were uniformly dispersed within the molecular sieve.

[0051] The catalysts prepared in Examples 1-5 and Comparative Examples 1-2 were characterized using high-resolution scanning electron microscopy and transmission electron microscopy, such as... Figure 2a -e and Figure 3a As shown in -e, this indicates that the prepared molecular sieve catalyst has a hierarchical porous structure, and the noble metal is uniformly dispersed within the molecular sieve. For example... Figure 2f -g and Figure 3fAs shown in -g, in the comparative examples, the molecular sieves synthesized without aminopropylsilicon source and using hydrothermal method showed no obvious hierarchical porous structure, and the noble metal content was low and unevenly distributed.

[0052] The catalysts prepared in Examples 1-5 and Comparative Examples 1-2 were respectively tableted, granulated, and sieved. 1.0 g of catalyst with a particle size of 20-40 mesh was weighed and packed into a fixed-bed reactor for the hydroisomerization reaction of n-hexane. First, the catalyst was activated by reduction under a hydrogen atmosphere at a flow rate of 50 mL / min, a reduction temperature of 400 °C, a reduction time of 2.0 h, and a pressure of atmospheric pressure. The activated catalyst was then subjected to the isomerization reaction of n-hexane at a reaction temperature of 300 °C, a reaction pressure of 2.0 MPa, and a hexane mass hourly space velocity of 1.0 h⁻¹. -1 The reaction performance of the catalyst was evaluated under the condition of a hydrogen-to-hydrogen molar ratio of 3:1, and the reaction results are shown in the table below.

[0053] catalyst hexane conversion rate hexane isomerization rate Reaction liquid yield Pd-1@ZSM-5(10) 72.4％ 71.3％ 90.3％ Pd-2@ZSM-5(10) 82.4％ 81.3％ 94.3％ Pd@ZSM-5(50) 81.9％ 80.7％ 96.6％ Pt@ZSM-5(100) 80.3％ 78.5％ 97.0％ Au@ZSM-5(50) 78.2％ 79.2％ 95.2％ Pd-3@ZSM-5(50) 65.6％ 76.7％ 85.3％ Pd-4@HT-ZSM-5 56.9％ 65.4％ 75.2％

[0054] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a macro-meso-microporous molecular sieve catalyst encapsulating noble metals, characterized in that, Includes the following steps: 1) Preparation of silicon-aluminum precursors loaded with noble metals A silicon source and an aluminum source are added to deionized water and stirred until homogeneous. Then, a noble metal precursor and an alkaline precipitant are added to make the system alkaline. Stirring continues, followed by filtration and drying to obtain a silicon-aluminum precursor loaded with noble metals. The silicon source contains amino-substituted silanes. 2) Preparation of macro-meso-microporous ZSM-5 molecular sieve catalysts encapsulated with noble metals The silica-alumina precursor loaded with noble metals obtained in step 1) was impregnated with an aqueous solution of a structure directing agent and dried and concentrated to obtain an initial gel; the initial gel was crystallized and then cooled to room temperature; the resulting solid product was washed with water, dried and calcined to obtain a macro-meso-microporous ZSM-5 molecular sieve catalyst encapsulating noble metals. The silicon source mentioned in step 1) is a mixture of silicon source I and silicon source II. Silicon source I is selected from aminopropyltriethoxysilane and / or aminopropyltrimethoxysilane, and silicon source II is selected from at least one of methyl orthosilicate, tetraethyl orthosilicate, silica sol and sodium silicate. The mass ratio of silicon source I to silicon source II is 1:100 to 1:

4. The catalyst contains 0.05%-5% precious metals. The concentration of the structure-directing agent aqueous solution in step 2) is 5-40%, and the mass ratio of the amount of structure-directing agent aqueous solution added to the silicon-aluminum precursor loaded with noble metal is 5-15:

1. In step 2), the crystallization conditions are 100~200°C. o Crystallize at C for 12-100 h.

2. The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to claim 1, characterized in that, The molar ratio of SiO2 to Al2O3 in the catalyst is 10-100.

3. The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to claim 1, characterized in that, The aluminum source mentioned in step 1) is at least one of aluminum isopropoxide, aluminum nitrate, aluminum chloride, and boehmite.

4. The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to claim 1, characterized in that, The noble metal precursor mentioned in step 1) is a soluble substance containing one of Pd, Pt, and Au, wherein the amount of the soluble substance containing one of Pd, Pt, and Au added is 0.1-10% of the mass of the silicon source.

5. The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to claim 1, characterized in that, The alkaline precipitant mentioned in step 1) is at least one of ammonia, sodium hydroxide, potassium hydroxide, ammonium carbonate, and ammonium bicarbonate, and the pH of the system is 9-11.

6. The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to claim 1, characterized in that, The structure directing agent mentioned in step 2) is at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrapropylammonium bromide and tetrapropylammonium chloride.

7. The method for preparing the macro-meso-microporous molecular sieve catalyst encapsulating noble metals according to claim 1, characterized in that, The drying temperature mentioned in step 2) is 30-100°C. o C, time is 2-12 hours, calcination temperature is 400-600℃ o C, the time is 2-8 hours.

8. The application of the macro-meso-microporous molecular sieve catalyst with encapsulated noble metal prepared by the method of any one of claims 1 to 7 in the hydroisomerization reaction of n-alkanes with a carbon number greater than or equal to 6.

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